Washington: Human feces contains gold, silver and other metals which could be worth hundreds of millions of dollars, say scientists who are investigating ways to extract the precious metals from poop.
Treated solid waste contains gold, silver and other metals, as well as rare elements such as palladium and vanadium that are used in electronics and alloys, researchers have found.
"There are metals everywhere, in your hair care products, detergents, even nanoparticles that are put in socks to prevent bad odours," said Dr Kathleen Smith, from the US Geological Survey (USGS).
Whatever their origin, the wastes containing these metals all end up being funnelled through wastewater treatment plants, where Smith said many metals end up in the leftover solid waste.
At treatment plants, wastewater goes through a series of physical, biological and chemical processes. The end products are treated water and biosolids.
Smith said more than 7 million tonnes of biosolids come out of US wastewater facilities each year. About half of that is used as fertiliser on fields and in forests, while the other half is incinerated or sent to landfills.
Smith and her team are on a mission to find out exactly what is in our waste.
"We have a two-pronged approach. In one part of the study, we are looking at removing some regulated metals from the biosolids that limit their use for land application," she said.
"In the other part of the project, we're interested in collecting valuable metals that could be sold, including some of the more technologically important metals, such as vanadium and copper that are in cell phones, computers and alloys," Smith said.
To do this, they are taking a page from the industrial mining operations' method book and are experimenting with some of the same chemicals, called leachates, which this industry uses to pull metals out of rock.
While some of these leachates have a bad reputation for damaging ecosystems when they leak or spill into the environment, Smith said that in a controlled setting, they could safely be used to recover metals in treated solid waste.
So far, her group has collected samples from small towns in the Rocky Mountains, rural communities and big cities.
In the treated waste, Smith's group has already started to discover metals like platinum, silver and gold. She stated that they have observed microscopic-sized metal particles in biosolids using a scanning electron microscope.
"The gold we found was at the level of a minimal mineral deposit," she said, meaning that if that amount were in rock, it might be commercially viable to mine it.
In a recent Environmental Science & Technology paper another research group also studying this issue calculated that the waste from 1 million Americans could contain as much as USD 13 million worth of metals.
The research was presented at the 249th national meeting of the American Chemical Society (ACS) in Denver.